1. Field of the Invention
This invention relates to improvements in a resonator type silencer installed in an intake system of an internal combustion engine or the like.
2. Description of the Prior Art
A resonator type silencer has been widely used in an intake system of an internal combustion engine in order to attenuate noise of intake air sucked into the engine. A typical resonator type silencer 51 is shown in FIG. 7 and includes a pair of case members 56, 56 usually made of a plastic and fabricated by an injection molding. Each case member 56 includes a cup-shaped section 55 having a bottom wall. A pipe section 54 is formed integral with the cup-shaped section 55 in a manner to pass through the bottom wall. The open ends 57 of the respective cup-shaped sections 55, 55 are brought into contact with and secured to each other, for example, by a vibration welding. The pipe sections 54, 54 are separate from each other inside the combined case members 56, 56. The pipe sections 54, 54 are connected to an air intake duct of the intake system. These separate pipe sections 54, 54 are connected to each other with a T-shaped connecting pipe or communication pipe 58 made of an elastomeric material such as a rubber. It will be understood that the T-shaped connecting pipe 58 is installed in position before combining the pair of case members 56, 56. Thus, an annular space 52 is formed around the pipe sections 54, 54 inside the cup-shaped section 55, 55. The annular space 52 is communicated with the inside the pipe sections 54, 54 thereby serving a resonance chamber to attenuate noise in the intake system.
However, drawbacks have been encountered in the above conventional resonance type silences in that the axes of the T-shaped pipe 58 and the pipe sections 54 unavoidably cannot be aligned under non-alignment of the axes of the case members 56, 56 during the welding of the open ends of the cup-shaped sections 55, 55. This forms an aperture or opening between the pipe section 54 and the T-shaped pipe 53. As a result, an air passage other than the communication pipe is unnecessarily formed, and therefore a predetermined resonance characteristics of the silencer is changed, thereby making it impossible to obtain an aimed resonance frequency for attenuating intake air noise. Additionally, since the T-shaped pipe is made of the elastomeric material, there is the possibility of being collapsed and deformed, thereby making the noise attenuating characteristics unstable. Furthermore, the welding of the open ends of the cup-shaped sections are made after the opposite ends of the T-shaped pipe are fitted on the opposite pipe sections, and therefore the operational efficiency of assembly of the silencer is degraded and it is difficult to maintain a precise fitting dimension of the T-shaped pipe to the pipe section, thus tending to produce a deflection or the like.